Method for transmitting ack/nack in wireless communication system and device using same

ABSTRACT

A method for transmitting a positive-acknowledgement/negative-acknowledgement (ACK/NACK) in a wireless communication system, performed by a wireless device, includes receiving a plurality of downlink (DL) grants on a plurality of serving cells, each DL grant including a counter downlink assignment index (DAI) and an ACK/NACK resource indicator (ARI), the counter DAI indicating an accumulative number of PDSCHs received by the wireless device for a corresponding DL grant, receiving a plurality of physical downlink shared channels (PDSCHs) associated with the plurality of DL grants, selecting one of a plurality of sets of PUCCH resources based on a payload size of uplink control information (UCI), the UCI including ACK/NACK bits for the plurality of PDSCHs, determining a PUCCH resource within the selected set of PUCCH resources based on an ARI included in the most recently received DL grant among the plurality of DL grants and transmitting the UCI by using a PUCCH format associated with the determined PUCCH resource.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.15/539,424 filed on Jun. 23, 2017, which was filed as the National Phaseof PCT International Application No. PCT/KR2015/014547, filed on Dec.31, 2015, which claims priority under 35 U.S.C. 119(e) to U.S.Provisional Application No. 62/098,347, filed on Dec. 31, 2014, No.62/161,225, filed on May 13, 2015, No. 62/161,869, filed on May 14,2015, No. 62/190,721, filed on Jul. 9, 2015, No. 62/203,922, filed onAug. 12, 2015, No. 62/209,310, filed on Aug. 24, 2015, No. 62/216,346,filed on Sep. 9, 2015, and No. 62/251,122, filed on Nov. 5, 2015, all ofwhich are hereby expressly incorporated by reference into the presentapplication.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to wireless communication, and moreparticularly, to a method of transmitting a positive-acknowledgement(ACK)/negative-acknowledgement (NACK) for hybrid automatic repeatrequest (HARQ) in a wireless communication system, and an apparatususing the method.

Discussion of the Related Art

Third generation partnership project (3GPP) long term evolution-advanced(LTE-A) is a technology which satisfies a bandwidth of at most 100 MHzand a data rate of at most 1 Gbps. Carrier aggregation (CA) is one oftechniques for increasing a maximum bandwidth by using a plurality ofcomponent carriers. One component carrier operates as one serving cell,and as a result, a terminal receives a service from a plurality ofserving cells.

With an increase in the number of supported serving cells, an amount offeedback information reported by the terminal is also increased. Thefeedback information includes channel state information (CSI), HARQACK/NACK, or the like.

A physical uplink control channel (PUCCH) is defined for transmission ofthe feedback information. The existing 3GPP LTE-A provides only threePUCCH formats (i.e., a PUCCH format 1/1a/1b, a PUCCH format 2/2a/2b, aPUCCH format 3) depending on a payload size.

With an increase in the number of serving cells supported in the CAenvironment, a greater number of PUCCH formats with different payloadsizes are required. In addition, how the terminal selects and uses thevarious PUCCH formats is an issue to be considered.

SUMMARY OF THE INVENTION

The present invention provides a method for transmitting an ACK/NACK ina wireless communication system, and an apparatus using the method.

In an aspect, a method for transmitting an ACK/NACK in a wirelesscommunication system is provided. The method includes receiving, by awireless device, downlink (DL) control information including a DL grantand an ACK/NACK resource indicator (ARI), receiving, by the wirelessdevice, a DL transport block based on the DL grant, selecting, by thewireless device, a physical uplink control channel (PUCCH) format basedon the ARI, determining, by the wireless device, a PUCCH resource forthe selected PUCCH format based on the ARI, and transmitting, by thewireless device, an ACK/NACK for the DL transport block by using theselected PUCCH format.

The wireless device may receive a plurality of DL grants from aplurality of cells, and may receive a plurality of DL transport blocksbased on the plurality of DL grants.

The PUCCH format may be selected as one of a first PUCCH format and asecond PUCCH format based on the ARI.

In another aspect, an apparatus for transmitting an ACK/NACK in awireless communication system includes a transceiver configured totransmit and receive a radio signal and a processor operatively coupledto the transceiver. The processor is configured to control thetransceiver to receive downlink (DL) control information including a DLgrant and an ACK/NACK resource indicator (ARI), control the transceiverto receive a DL transport block based on the DL grant, select a physicaluplink control channel (PUCCH) format based on the ARI, determine aPUCCH resource for the selected PUCCH format based on the ARI, andcontrol the transceiver to transmit an ACK/NACK for the DL transportblock by using the selected PUCCH format.

A method of transmitting uplink control information is provided when agreater number of serving cells are configured.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a subframe structure in 3^(rd) generation partnershipproject (3GPP) long term evolution-advanced (LTE-A).

FIG. 2 shows an example of performing hybrid automatic repeat request(HARQ).

FIG. 3 shows an example of a channel structure for a physical uplinkcontrol channel (PUCCH) format 1/1a/1b.

FIG. 4 shows an example of a channel structure for a PUCCH format2/2a/2b.

FIG. 5 shows an example of a channel structure for a PUCCH format 3.

FIG. 6 shows an example of a channel structure for an extended PUCCHformat.

FIG. 7 shows another example of a channel structure for an extendedPUCCH format.

FIG. 8 shows an example of selecting a PUCCH format according to anembodiment of the present invention.

FIG. 9 shows another example of selecting a PUCCH format according to anembodiment of the present invention.

FIG. 10 shows another example of selecting a PUCCH format according toan embodiment of the present invention.

FIG. 11 shows processing of positive-acknowledgement(ACK)/negative-acknowledgement (NACK) information according to anembodiment of the present invention.

FIG. 12 shows an example of selecting a PUCCH format according toanother embodiment of the present invention.

FIG. 13 shows another example of selecting a PUCCH format according toanother embodiment of the present invention.

FIG. 14 shows another example of selecting a PUCCH format according toanother embodiment of the present invention.

FIG. 15 shows an example of selecting a PUCCH format according toanother embodiment of the present invention.

FIG. 16 shows another example of selecting a PUCCH format according toanother embodiment of the present invention.

FIG. 17 shows another example of selecting a PUCCH format according toanother embodiment of the present invention.

FIG. 18 shows an example of selecting a PUCCH format according toanother embodiment of the present invention.

FIG. 19 shows another example of selecting a PUCCH format according toanother embodiment of the present invention.

FIG. 20 shows another example of selecting a PUCCH format according toanother embodiment of the present invention.

FIG. 21 shows an example of selecting a PUCCH format according toanother embodiment of the present invention.

FIG. 22 shows another example of selecting a PUCCH format according toanother embodiment of the present invention.

FIG. 23 shows another example of selecting a PUCCH format according toanother embodiment of the present invention.

FIG. 24 shows an example of selecting a PUCCH format.

FIG. 25 shows an example of selecting a PUCCH format.

FIG. 26 shows uplink control information (UCI) transmission according toan embodiment of the present invention.

FIG. 27 shows an example of selecting a PUCCH according to an embodimentof the present invention.

FIG. 28 shows another example of selecting a PUCCH according to anembodiment of the present invention.

FIG. 29 shows another example of selecting a PUCCH according to anembodiment of the present invention.

FIG. 30 shows an example of a cc-downlink assignment index (DAI).

FIG. 31 is a block diagram showing a wireless communication systemaccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A wireless device may be fixed or mobile, and may be referred to asanother terminology, such as a user equipment (UE), a mobile station(MS), a mobile terminal (MT), a user terminal (UT), a subscriber station(SS), a wireless device, a personal digital assistant (PDA), a wirelessmodem, a handheld device, etc. The wireless device may also be a devicesupporting only data communication such as a machine-type communication(MTC) device.

A base station (BS) is generally a fixed station that communicates withthe wireless device, and may be referred to as another terminology, suchas an evolved-NodeB (eNB), a base transceiver system (BTS), an accesspoint, etc.

Hereinafter, it is described that the present invention is appliedaccording to a 3^(rd) generation partnership project (3GPP) long termevolution (LTE)/LTE-advanced (LTE-A). However, this is for exemplarypurposes only, and thus the present invention is also applicable tovarious wireless communication networks.

The wireless device may be served by a plurality of serving cells. Eachserving cell may be defined with a downlink (DL) component carrier (CC)or a pair of a DL CC and an uplink (UL) CC. The plurality of servingcells may be managed by one BS, or may be managed by a plurality of BSs.The plurality of serving cells may be divided into a plurality of cellgroups.

The serving cell may be classified into a primary cell (PCell) and asecondary cell (SCell). The PCell operates at a primary frequency, andis a cell designated as the PCell when an initial network entry processis performed or when a network re-entry process starts or in a handoverprocess. The PCell is also called a reference cell. The SCell operatesat a secondary frequency. The SCell may be configured after a radioresource control (RRC) connection is established, and may be used toprovide an additional radio resource. At least one PCell is configuredalways. The SCell may be added, modified, or released by usinghigher-layer signaling (e.g., an RRC message).

A cell index (CI) of the primary cell may be fixed. For example, alowest CI may be designated as a CI of the primary cell. It is assumedhereinafter that the CI of the primary cell is 0 and a CI of thesecondary cell is allocated sequentially starting from 1.

FIG. 1 shows a subframe structure in 3GPP LTE-A.

A radio frame includes 10 subframes indexed with 0 to 9. One subframeincludes 2 consecutive slots. A time required for transmitting onesubframe is defined as a transmission time interval (TTI). For example,one subframe may have a length of 1 millisecond (ms), and one slot mayhave a length of 0.5 ms.

A subframe may include a plurality of orthogonal frequency divisionmultiplexing (OFDM) symbols. Since the 3GPP LTE uses orthogonalfrequency division multiple access (OFDMA) in a downlink (DL), the OFDMsymbol is only for expressing one symbol period in the time domain, andthere is no limitation in a multiple access scheme or terminologies. Forexample, the OFDM symbol may also be referred to as another terminologysuch as a single carrier frequency division multiple access (SC-FDMA)symbol, a symbol period, etc.

Although it is described that one slot includes 14 OFDM symbols forexample, the number of OFDM symbols included in one slot may varydepending on a length of a cyclic prefix (CP). According to 3GPP LTE-A,in case of a normal CP, one slot includes 14 OFDM symbols, and in caseof an extended CP, one slot includes 12 OFDM symbols.

A resource block (RB) is a resource allocation unit, and includes aplurality of subcarriers in one slot. For example, if one slot includes7 OFDM symbols in a time domain and the RB includes 12 subcarriers in afrequency domain, one RB may include 7×12 resource elements (REs).

A physical channel of 3GPP LTE-A may be classified into a downlink (DL)physical channel and an uplink (UL) physical channel. The DL physicalchannel includes a physical downlink control channel (PDCCH), a physicalcontrol format indicator channel (PCFICH), a physical hybrid-ARQindicator channel (PHICH), and a physical downlink shared channel(PDSCH).

The PCFICH transmitted in a first OFDM symbol of the subframe carries acontrol format indicator (CFI) regarding the number of OFDM symbols(i.e., a size of the control region) used for transmission of controlchannels in the subframe. A wireless device first receives the CFI onthe PCFICH, and thereafter monitors the PDCCH.

The PHICH carries a positive-acknowledgement(ACK)/negative-acknowledgement (NACK) signal for an uplink hybridautomatic repeat request (HARQ). The ACK/NACK signal for uplink (UL)data on a PUSCH transmitted by the wireless device is transmitted on thePHICH.

Control information transmitted through the PDCCH is referred to asdownlink control information (DCI). The DCI may include resourceallocation of the PDSCH (this is referred to as a downlink (DL) grant),resource allocation of a PUSCH (this is referred to as an uplink (UL)grant), a set of transmit power control commands for individual UEs inany UE group, and/or activation of a voice over Internet protocol(VoIP).

The UL physical channel includes a physical uplink control channel(PUCCH) and a physical uplink shared channel (PUSCH). The PUCCH isallocated in an RB pair in a subframe. RBs belonging to the RB pairoccupy different subcarriers in each of a 1^(st) slot and a 2^(nd) slot.The PUSCH is allocated by a UL grant on the PDCCH. In a normal CP, a4^(th) OFDM symbol of each slot is used in transmission of ademodulation reference signal (DMRS) for the PUSCH.

Uplink control information (UCI) includes at least any one of HARQACK/NACK, channel state information (CSI), and a scheduling request(SR). Hereinafter, as an indicator for indicating a state of a downlink(DL) channel, the CSI may include at least any one of a channel qualityindicator (CQI) and a precoding matrix indicator (PMI).

In order to transmit a variety of UCI on a PUCCH, a combination betweenthe UCI and the PUCCH is defined as a PUCCH format as shown in thefollowing table.

TABLE 1 PUCCH format UCI to be transmitted PUCCH format 1 Positive SRPUCCH format 1a/1b 1-bit or 2-bit HARQ ACK/NACK PUCCH format 2 CSIreport PUCCH format 2a/2b CSI report and 1-bit or 2-bit HARQ ACK/NACKPUCCH format 3 HARQ ACK/NACK, SR, CSI

The PUCCH format 1a/1b is used to carry the 1-bit or 2-bit HARQ ACK/NACKby using binary phase shift keying (BPSK) modulation or quadrature phaseshift keying (QPSK) modulation.

The PUCCH format 3 is used to carry encoded UCI of 48 bits. The PUCCHformat 3 may carry HARQ ACK/NACK for a plurality of serving cells and aCSI report for one serving cell.

FIG. 2 shows an example of performing HARQ.

A wireless device monitors a PDCCH, and receives a DL grant including aDL resource allocation on a PDCCH 201 (or EPDDCH) in a DL subframe n.The wireless device receives a DL transport block through a PDSCH 202indicated by the DL resource allocation.

The wireless device transmits an ACK/NACK signal for the DL transportblock on a PUCCH 210 in a UL subframe n+4. The ACK/NACK signalcorresponds to an ACK signal when the DL transport block is successfullydecoded, and corresponds to a NACK signal when the DL transport blockfails in decoding. Upon receiving the NACK signal, a BS may retransmitthe DL transport block until the ACK signal is received or until thenumber of retransmission attempts reaches its maximum number.

In 3GPP LTE-A, 3 types of PUCCH formats (i.e., a PUCCH format 1/1a/1b, aPUCCH format 2/2a/2b, a PUCCH format 3) are used to carry an ACK/NACKsignal which is a reception acknowledgement for HARQ. All PUCCH formatsuse different resource blocks in two slots.

FIG. 3 shows an example of a channel structure for a PUCCH format1/1a/1b.

One slot includes 7 OFDM symbols. 3 OFDM symbols in the middle arereference signal (RS) OFDM symbols for DMRS. The remaining 4 OFDMsymbols are data OFDM symbols for UCI.

A data symbol d(0) is first spread in a frequency domain by using afrequency-domain sequence R(i)={r(0), r(1), r(2), r(3), r(4), r(5),r(6), r(7), r(8), r(9), r(10), r(11)}. The frequency-domain spreadingincludes that r(i) corresponds to each subcarrier in a resource block.Although not shown, a frequency-domain sequence in each OFDM symbol maybe generated by being cyclically shifted by a cyclic shift vale from abasis sequence. The cyclic shift value may be acquired on the basis of acorresponding OFDM symbol index.

The sequence generated by being spread in the frequency domain is spreadagain in a time domain by using an orthogonal code W(j)={w(0), w(1),w(2), w(3)}. The time-domain spreading includes that w(i) corresponds toeach OFDM symbol in a slot.

The data symbol d(0) is used equally in a first slot and a second slot.The PUCCH format 1a uses binary phase shift keying (BPSK) for a datasymbol, and carries 1-bit ACK/NACK. The PUCCH format 1b uses quadraturephase shift keying (QPSK) for a data symbol, and carries 2-bit ACK/NACK.

FIG. 4 shows an example of a channel structure for a PUCCH format2/2a/2b.

One slot includes 7 OFDM symbols. 2^(nd) and 6^(th) OFDM symbols are RSOFDM symbols for DMRS. The remaining 5 OFDM symbols are data OFDMsymbols for UCI.

The PUCCH format 2/2a/2b uses only frequency-domain spreading withouttime-domain spreading. The frequency-domain spreading is achieved byusing a frequency-domain sequence R(i)={r(0), r(1), r(2), r(3), r(4),r(5), r(6), r(7), r(8), r(9), r(10), r(11)}. The frequency-domainspreading includes that r(i) corresponds to each subcarrier in aresource block. Although not shown, a frequency-domain sequence in eachOFDM symbol may be generated by being cyclically shifted by a cyclicshift vale from a basis sequence. The cyclic shift value may be acquiredon the basis of a corresponding OFDM symbol index.

5 data symbols may be transmitted in each slot. Therefore, 10 datasymbols d(0) to d(9) may be transmitted in one subframe. When usingQPSK, the PUCCH format 2/2a/2b may carry 20 encoded bits. Although notshown, ACK/NACK is transmitted by using a phase offset of 2 RS OFDMsymbols. The PUCCH format 2a uses BPSK for a phase offset, and carries1-bit ACK/NACK. The PUCCH format 2b uses QPSK for a phase offset, andcarries 2-bit ACK/NACK.

FIG. 5 shows an example of a channel structure for a PUCCH format 3.

One slot includes 7 OFDM symbols. 2^(nd) and 6^(th) OFDM symbols are RSOFDM symbols for DMRS. The remaining 5 OFDM symbols are data OFDMsymbols for UCI.

The PUCCH format 3 may carry 24 data symbols d(0) to d(23). When usingQPSK, the PUCCH format 3 may carry 48 encoded bits.

In a first slot, first 12 data symbols d(0) to d(11) are spread in atime domain by using an orthogonal code W(j)={w(0), w(1), w(2), w(3),w(4)}. The time-domain spreading includes that w(i) corresponds to eachOFDM symbol in a slot. In a second slot, second 12 data symbols d(12) tod(23) are spread in the time domain by using the orthogonal code W(j).

A time/frequency/code resource used in PUCCH transmission is called aPUCCH resource. For example, an orthogonal code index, a cyclic shiftindex, and a resource block index are required for the PUCCH format1/1a/1b. A cyclic shift index and a resource block index are requiredfor the PUCCH format 2/2a/2b. An orthogonal code index and a resourceblock index are required for the PUCCH format 2/2a/2b. A resource indexis a parameter used to determine a corresponding PUCCH resource.

A resource index for the PUCCH format 1a/1b for ACK/NACK is given by acorresponding DL grant. Although a resource index for the PUCCH format 3for ACK/NACK is given by a corresponding DL grant, this is designated ina pre-designated resource index set. For example, a BS pre-designates 4resource indices for the PUCCH format 3 through an RRC message. Inaddition, one of the 4 resource indices may be designated through aresource indicator in a DL grant (this is called an ‘ACK/NACK resourceindicator (ARI)’). If the ARI is 2 bits, it may be defined as follows.

TABLE 2 ARI value PUCCH resource 00 first PUCCH resource index 01 secondPUCCH resource index 10 third PUCCH resource index 11 fourth PUCCHresource index

A size of UCI payload that can be carried using the PUCCH format 3 is atmost 21 bits. The UCI payload includes the number of information bitsbefore being encoded. However, with an increase in the number of servingcells configured for the wireless device, a required UCI payload sizemay be more increased.

First, a channel structure of a PUCCH format for the increased UCIpayload is described.

For convenience, the PUCCH format for UCI transmission is defined asfollows.

1) PUCCHx: A PUCCH format for 1-bit or 2-bit UCI transmission (e.g., aPUCCH format 1/1a/1b)

2) PUCCHy: A PUCCH format for UCI transmission of at most M bits (M>2)(e.g., a PUCCH format 3)

3) PUCCHz: A PUCCH format for UCI transmission exceeding M bits. This isalso referred to as an extended PUCCH format.

FIG. 6 shows an example of a channel structure for an extended PUCCHformat.

One slot includes 7 OFDM symbols. An OFDM symbol in the middle (i.e., a4^(th) OFDM symbol) is an RS OFDM symbol for DMRS. The remaining 6 OFDMsymbols are data OFDM symbols for UCI. If one slot includes 6 OFDMsymbols, a 3^(rd) OFDM symbol is an RS OFDM symbol, and the remaining 5OFDM symbols are data OFDM symbols.

The extended PUCCH format does not use frequency-domain spreading andtime-domain spreading. When one resource is allocated to the extendedPUCCH format, 12 data symbols may be transmitted for each OFDM symbol.Therefore, 144 data symbols d(O) to d(143) may be transmitted in onesubframe. When using QPSK, the extended PUCCH format may carry 288encoded bits.

FIG. 7 shows another example of a channel structure for an extendedPUCCH format.

In comparison with the channel structure of FIG. 6, 6 data symbols arerepeated in one resource block for each OFDM symbol. For example, {d(0),d(1), d(2), d(3), d(4), d(5), d(0), d(1), d(2), d(3), d(4), d(5)} istransmitted in a first OFDM symbol. Accordingly, although 144 datasymbols can be transmitted in the channel structure of FIG. 6, 72 datasymbols d(O) to d(71) may be transmitted in this channel structure. Whenusing QPSK, the extended PUCCH format may carry 144 encoded bits.

In order to support multi-user multiplexing, code division multiplexing(CDM) may be supported in a data symbol repeated in each OFDM symbol.For example, {+d(0), +d(1), +d(2), +d(3), +d(4), +d(5), +d(0), +d(1),+d(2), +d(3), +d(4), d(5)} may be transmitted through CDM 0, and {+d(0),+d(1), +d(2), +d(3), +d(4), +d(5), −d(0), −d(1), −d(2), −d(3), −d(4),−d(5)} may be transmitted through CDM 1. A cyclic shift value used inDMRS may vary depending on the CDM.

For convenience, the channel structure of FIG. 6 is denoted by PUCCHz1,the channel structure of FIG. 7 is denoted by PUCCHz2, and thesechannels are collectively denoted by PUCCHz.

A plurality of resource blocks may be allocated to the PUCCHz. That is,only one resource block may be allocated to the existing PUCCHx/y,whereas one or more resource blocks may be allocated to the PUCCHz. Thismeans that a bandwidth at which the PUCCHz is transmitted is the same asor greater than a bandwidth at which the PUCCHx/y is transmitted.

A BS may inform each wireless device of an indication regarding whetherto use the PUCCHz1 or the PUCCHz2. Each wireless device may confirmwhether to use a corresponding PUCCH format through a resourceconfiguration of the PUCCHz1 or a resource configuration of the PUCCHz2.The BS may instruct to use both the PUCCHz1 and the PUCCHz2. Thewireless device may select one of the PUCCHz1 and the PUCCHz2 accordingto a criterion for selecting a PUCCH format described below.

Similarly to the configuration of the PUCCH format 3, in the resourceconfiguration for the PUCCHz, a plurality of candidate resources may beconfigured in advance through an RRC message, and one of the pluralityof candidate resources may be designated through a DL grant.

Now, a criterion for selecting a PUCCH format used in UCI transmissionfrom a plurality of PUCCH formats is described. Although it is describedhereinafter that one of the PUCCHy and the PUCCHz is selected forexample, it is also possible to select one of the PUCCHx and the PUCCHzor to select one of the PUCCHz, the PUCCHy, and the PUCCHz.

A plurality of selectable PUCCH formats may include a plurality of PUCCHformats having different resource blocks. Alternatively, the pluralityof selectable PUCCH formats may include a plurality of PUCCH formatshaving different bandwidths. For example, one of a first PUCCHz havingone resource block and a second PUCCHz having two resource blocks may beselected.

Selection of PUCCH Format Using DCI

FIG. 8 shows an example of selecting a PUCCH format according to anembodiment of the present invention.

A PUCCH format used by a wireless device is reported through DCItransmitted in each serving cell. The DCI may include a PUCCH formatindication (PFI) for reporting the PUCCH format and an ARI for reportinga resource of the PUCCH format.

The PFI may include information for identifying which format will beused between PUCCHy and PUCCHz. Each of a plurality of availablecandidate PUCCHy resources and candidate PUCCHz resources may beconfigured, and an ARI may designate one of a plurality of PUCCHresources for the selected PUCCH format.

The PFI may be transmitted only through DCI of an SCell other than DCIof a PCell, and may indicate the same value with respect to the samewireless device. It is shown herein that DCI of a cell 0 (PCell) has aPFI for designating PUCCHy, and DCI of a cell 1 (SCell) has a PFI fordesignating PUCCHy.

FIG. 9 shows another example of selecting a PUCCH format according to anembodiment of the present invention. It shows that DCI of a cell 1/2/3has a PFI for designating PUCCHz.

FIG. 10 shows another example of selecting a PUCCH format according toan embodiment of the present invention. It is shown herein that DCI of acell 0 (PCell) has a PFI for designating PUCCHz, and DCI of a cell 2(SCell) has a PFI for designating PUCCHz.

In order to designate the PUCCH format, bit extension orreinterpretation of an ARI is also possible, rather than an independentfield such as the PFI. Alternatively, the PUCCH format may be reportedthrough a search space, a scrambling sequence, a cyclic redundancy check(CRC) masking sequence, or the like in which the DCI is transmitted.

An ARI value may designate a combination of the PUCCH format and thePUCCH resource. For example, if a 2-bit ARI is reused, it may beexpressed as follows.

TABLE 3 ARI value PUCCH resource 00 first PUCCH resource index of PUCCHy01 second PUCCH resource index of PUCCHy 10 first PUCCH resource indexof PUCCHz 11 second PUCCH resource index of PUCCHz

When a plurality of selectable PUCCH formats include a plurality ofPUCCH formats having different resource blocks, an ARI designates adifferent number of resource blocks to select a corresponding PUCCHformat. For example, if there are a first PUCCHz having one resourceblock and a second PUCCHz having two resource blocks and if the ARIindicates two resource blocks, the second PUCCH format may be selected.

FIG. 11 shows processing of ACK/NACK information according to anembodiment of the present invention. This may be processing of ACK/NACKinformation applied to PUCCHz.

In step S310, it is assumed that the ACK/NACK information is a Q-bitsequence {a₀, . . . , a_(Q−1)}. a_(q) is an ACK/NACK bit. Q cannotexceed a maximum payload of the PUCCHz.

In step S320, an ACK/NACK information sequence is encoded according to acode rate. A well-known tail-biting convolutional code (TBCC) or thelike may be applied as an encoding scheme.

In step S330, an encoded bit is modulated according to a modulationscheme to generate a plurality of data symbols {d₀, . . . , d_(K)}.

To generate ACK/NACK information for a plurality of cells, the followingterms are defined for convenience of explanation.

-   -   Mi: The number of DL subframes linked to transmit ACK/NACK        through a corresponding UL subframe for a cell i.    -   Nc: The number of PDSCHs capable of transmitting an ACK/NACK        feedback for a PUCCH format. Spatial bundling may or may not be        applied. When a plurality of transport blocks are transmitted on        one PDSCH, if one ACK/NACK bit corresponds to each transport        block, it is said that the spatial bundling is not applied. When        a plurality of transport blocks are transmitted on one PDSCH, if        one ACK/NACK bit corresponds to the plurality of transport        blocks, it is said that the spatial bundling is applied.

<If it is configured only with an FDD cell, or if a cell fortransmitting a PUCCH is the FDD cell, or if Mi=1>

(1) ACK/NACK bits may be arranged in order of a ‘c-DAI’. ACK/NACKinformation includes Nc ACK/NACK bits corresponding to a PDSCH withc-DAI<=Nc. The ‘c-DAI’ is described below.

(2) ACK/NACK bits may be arranged in order of a cell index. ACK/NACKinformation may include ACK/NACK bits for Nc cells in an ascending orderof the cell index.

<If a cell satisfying Mi>1 is present>

(1) A wireless device alternately arranges an ACK/NACK bit correspondingto each cell in such a manner that ACK/NACK bits for a plurality ofcells corresponding to one subframe are first arranged.

(1-1) The ACK/NACK bits may be arranged in order of a c-DAI. A cellhaving a small c-DAI value is selected preferentially for a determinedPUCCH format, and ACK/NACK information includes at most Nc ACK/NACK bitscorresponding to Mi subframes of each cell. If the wireless devicemisses reception of the c-DAI, the ACK/NACK information may bemismatched with respect to a BS. To avoid this, the ACK/NACK bit may bearranged by assuming a maximum value among values of Mi for all cells asMi of each cell. A maximum c-DIA value capable of performing ACK/NACKtransmission may be predetermined or may be calculated according tocapacity Nc of each PUCCH format.

(1-2) The ACK/NACK bit may be arranged in an order pre-assigned for eachPUCCH format. The ACK/NACK information may include at most Nc ACK/NACKbits corresponding to Mi subframes of each cell in an ascending order ofthe cell index.

In the method (1-1) or (1-2), if capacity of ACK/NACK information thatcan be transmitted with a corresponding PUCCH format is insufficient,ACK/NACK information of a last-order cell may be transmitted only forsome subframes among Mi subframes.

(2) The wireless device first arranges ACK/NACK bits for a plurality ofsubframes corresponding to respective cells. A t-DAI is described below.For all serving cells or serving cells with Mi>1, the ACK/NACKinformation may be configured on the basis of an ACK/NACK bitcorresponding to at most Msf subframes. Msf is a number determined foreach PUCCH format. A method of selecting the Msf subframes may includeselecting preferentially a temporally preceding subframe or selectingpreferentially a subframe scheduled with a small t-DAI. If capacity ofACK/NACK information that can be transmitted with a corresponding PUCCHformat is insufficient, it may be transmitted only for some subframesamong the Msf subframes of the last-order cell.

(3) The wireless device may transmit preferentially the ACK/NACK bitcorresponding to at most Msf subframes with respect to at most Mcellcells as ACK/NACK information. Msf and Mcell are numbers determined foreach PUCCH format. A method of selecting the Msf subframes may includeselecting preferentially a temporally preceding subframe or selectingpreferentially a subframe scheduled with a small t-DAI.

When the ACK/NACK information cannot be transmitted through thedetermined PUCCH format, the wireless device may perform the followingoperation.

-   -   Since it may be determined that there is an error in reception        of DCI for designating the PUCCH format, the entire ACK/NACK        information is not transmitted. Only ACK/NACK may be transmitted        for a specific cell (e.g., PCell) which does not require an        indication of the PUCCH format through the DCI.    -   Only the remaining ACK/NACK information other than ACK/NACK for        a corresponding PDSCH is transmitted by using the designated        PUCCH format.    -   The ACK/NACK information is transmitted through compression of        the number of ACK/NACK bits by using bundling (e.g., AND        operation) or the like of the ACK/NACK bit. Whether to compress        ACK/NACK may be reported through CRC masking of the ACK/NACK        information together with a corresponding PUCCH format.

Since a subframe in which the PUCCH is to be transmitted is designatedas a subframe for transmitting CSI, the PUCCH format may have totransmit the CSI together with ACK/NACK. This means that the number ofACK/NACK bits that can be transmitted is reduced. The followingoperation may be performed when the total number of bits of UCI to betransmitted with the PUCCH format is greater than the number of bitsthat can be transmitted with an indicated PUCCH format.

-   -   The wireless device determines that there is an error in DCI        reception having a PFI, and thus does not transmit the entire        ACK/NACK. Only ACK/NACK may be transmitted for a specific cell        (e.g., PCell) which does not require an indication of the PUCCH        format through the DCI.    -   If capacity of the PUCCH format is Nc bits and the number of        bits for CSI is Ncsi, ACK/NACK information of (Nc-Ncsi) bits is        transmitted together with the CSI. A cell for transmitting        ACK/NACK information may be determined according to a cell index        order.

The wireless device may abandon the CSI transmission and transmit onlythe ACK/NACK information. When a sum of the number of CSI bits and thenumber of ACK/NACK bits for all cells is less than or equal to themaximum number of information bits that can be transmitted with PUCCHz,ACK/NACK and CSI are both transmitted. If the sum exceeds the maximumnumber, CSI transmission may be abandoned and only ACK/NACK may betransmitted.

PUCCH format selection based on cell/subframe in which PDSCH is received

A wireless device may determine a PUCCH format to be used according to arange of a serving cell corresponding to an ACK/NACK feedback. The rangeof the serving cell and the PUCCH format to be applied may bepredetermined or may be given through RRC signaling.

For example, assume that K serving cells are configured for the wirelessdevice. PUCCHy may be used to feed back ACK/NACK for cells from a cell 0to a cell L−1 (L<K), and PUCCHz may be used to feed back ACK/NACK forcells from a cell L to a cell K−1.

A BS may predetermine a plurality of candidate resources for the PUCCHyand a plurality of candidate resources for the PUCCHz through RRCsignaling. In addition, which one will be used among the plurality ofcandidate resources may be designated through an ARI in DCI.

Specifically, assume that a cell group corresponding to both the PUCCHyand the PUCCHz is a cell group y, and a cell group corresponding to onlythe PUCCHz is a cell group z.

FIG. 12 shows an example of selecting a PUCCH format according toanother embodiment of the present invention.

An ARI in DCI of a cell group y and an ARI in DCI of a cell group z bothindicate the same value. A wireless device selects a resource indicatedby the ARI among a plurality of candidate resources for a PUCCH formatselected by the wireless device. Herein, since only DCI of a cell incell group y is received, the wireless device selects PUCCHy.

FIG. 13 shows another example of selecting a PUCCH format according toanother embodiment of the present invention. In comparison with theexample of FIG. 12, a wireless device receives DCI from a cell 1 of acell group y and a cell 2/3 of a cell group z. Since the cell group zcan use only PUCCHz, the wireless device selects the PUCCHz.

FIG. 14 shows another example of selecting a PUCCH format according toanother embodiment of the present invention. In comparison with theexample of FIG. 12, a wireless device receives DCI from a cell 0 of acell group y and a cell 2 of a cell group z. Since the cell group z canuse only PUCCHz, the wireless device selects the PUCCHz.

FIG. 15 shows an example of selecting a PUCCH format according toanother embodiment of the present invention.

An ARI in DCI of a cell group y indicates a resource allocated toPUCCHy, and an ARI in DCI of a cell group z indicates a resourceallocated to PUCCHz. Upon receiving the DCI of the cell group z, awireless device ignores the ARI in the DCI of the cell group y, andselects a resource of the PUCCHz by using the ARI in the DCI of the cellgroup z. Herein, since only DCI of a cell in the cell group y isreceived, the wireless device selects PUCCHy.

FIG. 16 shows another example of selecting a PUCCH format according toanother embodiment of the present invention. In comparison with theexample of FIG. 15, a wireless device receives DCI from a cell 1 of acell group y and a cell 2/3 of a cell group z. An ARI of the cell groupy is ignored, and a PUCCHz resource indicated by an ARI of a cell groupz is selected.

FIG. 17 shows another example of selecting a PUCCH format according toanother embodiment of the present invention. In comparison with theexample of FIG. 15, a wireless device receives DCI from a cell 0 of acell group y and a cell 2 of a cell group z. An ARI of the cell 0 isignored, and a PUCCHz resource indicated by an ARI of the cell 2 isselected.

In a case where PUCCHz uses a plurality of PUCCHy resources (e.g., aplurality of resource blocks are allocated to PUCCHz), a PUCCHy resourceto be used for ACK/NACK transmission may be pre-designated for each cellgroup, and PUCCHz may be transmitted by using the PUCCHy resource.

When it is assumed that N PUCCHy resources can be used simultaneouslyfor at most N cell groups, a PUCCH resource may be selected by using anARI in the following manner.

FIG. 18 shows an example of selecting a PUCCH format according toanother embodiment of the present invention.

An ARI indicates one of combinations of N PUCCHy resources. An ARI valueand a combination of N PUCCHy resources may be predetermined or may beconfigured by RRC signaling. ARIs of all cell groups indicate the samevalue, and a wireless device may transmit ACK/NACK by using only anecessary PUCCHy resource among combinations of PUCCHy resourcesindicated by the ARIs.

Herein, a PUCCH resource corresponding to a cell group y1 is calledPUCCHy1, and a PUCCH resource corresponding to a cell group y2 is calledPUCCHy2. A cell 0 and a cell 1 belong to the cell group y1, and ARI=2.Therefore, a third resource of the PUCCHy1 is selected.

FIG. 19 shows another example of selecting a PUCCH format according toanother embodiment of the present invention. In comparison with theexample of FIG. 18, ARIs of a cell 1, a cell 2, and a cell 3 are all thesame value. A second resource of PUCCHy1 is selected in the cell 1, anda second resource of PUCCHy2 is selected in the cell 2/3.

FIG. 20 shows another example of selecting a PUCCH format according toanother embodiment of the present invention. In comparison with theexample of FIG. 18, a first resource of PUCCHy1 is selected in a cell 0,and a first resource of PUCCHy2 is selected in a cell 2.

FIG. 21 shows an example of selecting a PUCCH format according toanother embodiment of the present invention.

A plurality of available candidate PUCCHy resources are allocated toeach cell group in advance through RRC signaling. An ARI of each cellgroup indicates one of a plurality of candidate PUCCHy resources of acorresponding cell group. ARIs of the same cell group are all set to thesame value. A wireless device selects a PUCCHy resource designated bythe ARI to transmit ACK/NACK.

Herein, a plurality of PUCCHy1 resources for a cell group y1 and aplurality of PUCCHy2 for a cell group y2 are predefined. A cell 0 and acell 1 belong to the cell group y1, and ARI=2. Therefore, a thirdresource is selected among the plurality of PUCCHy1 resources.

FIG. 22 shows another example of selecting a PUCCH format according toanother embodiment of the present invention. In comparison with theexample of FIG. 21, a third resource is selected among a plurality ofPUCCHy1 resources in a cell 1 in a cell group y1, and a second resourceis selected among a plurality of PUCCH2 resources in a cell 2/3 in acell group y2.

FIG. 23 shows another example of selecting a PUCCH format according toanother embodiment of the present invention. In comparison with theexample of FIG. 21, a third resource is selected among a plurality ofPUCCHy1 resources in a cell 0 in a cell group y1, and a third resourceis selected among a plurality of PUCCHy2 resources in a cell 2 in a cellgroup y.

If a PUCCH format is determined according to a cell/subframe in which aPUSCH is received, ACK/NACK information may be configured as follows.

<If it is configured only with an FDD cell, or if a cell fortransmitting a PUCCH is the FDD cell, or if Mi=1>

ACK/NACK information may include an ACK/NACK bit arranged in an orderpre-assigned for each PUCCH format. Mcell may be defined for each PUCCHformat. If Cidmax denotes a maximum cell index of a cell in which awireless device receives a PDSCH, a PUCCH format may be selected whichis smaller than Cidmax+1 and corresponds to a smallest Mcell. For eachPUCCH format, Mcell may be designated as Mcell=Nc.

The PUCCH format transmits ACK/NACK information corresponding to Mcellcells in an ascending order of a cell index or ACK/NACK informationcorresponding to Mcell cells in which Mi is not 0 in the ascending orderof the cell index.

<If a cell satisfying Mi>1 is present>

(1) Cell unit transmission: The wireless device may select a PUCCHformat on the basis of a PDSCH-scheduled cell or cell group.

ACK/NACK bits may be arranged in an order pre-assigned for each PUCCHformat. Mcell may be defined for each PUCCH format. When Cidmax denotesa maximum cell index of a cell in which the wireless receives a PDSCH, aPUCCH format corresponding to a smallest value Nc where Mcell>=Cidmaxmay be selected. A Mcell value of the PUCCH format may be designated asa greatest value satisfying that a sum of values of Mi for all cells ofwhich a cell index is less than or greater than Mcell or a sum of valuesof Mi for all cells of which a cell index is less than or greater thanMcell−1 is less than or equal to Nc.

The wireless device may select preferentially cells having a small cellindex or cells of which Mi is not 0 among the cells having the smallcell index, and may transmit an ACK/NACK bit corresponding to Misubframes through a corresponding PUCCH format at most a maximum totalsum Nc.

FIG. 24 shows an example of selecting a PUCCH format. Among indices ofcells in which a wireless device receives a PDSCH, a maximum index is 3.The wireless device selects a PUCCH format having a smallest value Ncgreater than or equal to M1+M2+M3=9.

If a size of ACK/NACK information exceeds capacity of the PUCCH format,ACK/NACK information of a last-order cell may be transmitted only insome of Mi subframes.

(2) Cell-subframe combination unit transmission: The wireless device mayselect a PUCCH format based on a combination of <PDSCH-scheduled cell orcell group> and <PDSCH-scheduled subframe or t-DAI>.

ACK/NACK bits may be arranged in an order pre-assigned for each PUCCHformat. Mcell and Msf may be defined for each PUCCH format. Assume thatCidmax denotes a maximum cell index of a cell in which a PDSCH isreceived by a wireless device, t-DAImax denotes a maximum value amongvalues of t-DAI received by the wireless device. A PUCCH format having asmallest Nc may be selected when the Mcell value is greater than orequal to Cidmax, and the Msf value is greater than or equal to t-DAImax.Mcell and Msf may be defined in the range of Mcell*Msf<=Nc.

A UE may select preferentially a subframe corresponding to a small t-DAIas a subframe for transmitting ACK/NACK for each cell. Alternatively, acell having a smallest cell index may be selected preferentially.

FIG. 25 shows an example of selecting a PUCCH format. A maximum cellindex of a cell in which a wireless device receives a PDSCH is 3. Sincea maximum t-DAI value is 2, a PUCCH format corresponding to a smallestNc value may be selected while supporting Mcell>=3 and Msf>=2.

In the aforementioned embodiment, the PUCCH format may be selectedaccording to an activated cell. The ACK/NACK information may includeonly an ACK/NACK bit for the activated cell. An ARI may be used only todetermine validity of DCI having the ARI.

In the aforementioned embodiment, Nc, Mmax, and Cidmax may be calculatedor excluded from a criterion for selecting the PUCCH format under theassumption that a first subframe of a specific cell is alwaystransmitted exceptionally in a UCI payload configuration for the PUCCH.An ACK/NACK bit corresponding to the first subframe of the specific cellmay be always arranged at a fixed position in the ACK/NACK information.

The ARI may indicate a PUCCH format and/or a PUCCH resource to transmitthe ACK/NACK information. The ARI may indicate the number of bits ofACK/NACK information and/or whether to perform bundling on ACK/NACK. Adifferent ARI may indicate a combination of the same PUCCHz resourcesand the number of bits of different ACK/NACK information, or mayindicate a combination of different PUCCHz resources and the number ofbits of different ACK/NACK information.

FIG. 26 shows UCI transmission according to an embodiment of the presentinvention.

CSI transmission may be triggered in a subframe in which ACK/NACKinformation is to be transmitted. The CSI transmission may be triggeredthrough a periodic CSI report or a DCI-based indication.

If the PUCCH format transmits both the ACK/NACK information and the CSI,the PUCCH format may be determined by considering a CSI payload size.

For example, assume that PUCCHy may be used to transmit L ACK/NACK bits,or ACK/NACK bits corresponding to L cells, and PUCCHz may be used totransmit more than L ACK/NACK bits. Also, assume that a CSI payload sizeis n bits. Then, in a subframe in which the CSI and the ACK/NACKinformation are transmitted, the PUCCH format may be selected on thebasis of ACK/NACK bits of up to L-n bits and/or ACK/NACKA bits exceedingthe L-n bits.

If PUCCHz is selected, CSI transmission may be abandoned and only theACK/NACK information may be transmitted.

If a sum of the number of ACK/NACK bits for all cells and the number ofCSI bits is less than or equal to the maximum number of information bitsthat can be transmitted on PUCCHz, then both the ACK/NACK and the CSImay be transmitted through the PUCCHz. If the sum exceeds the maximumvalue, CSI transmission may be abandoned and only the ACK/NACK may betransmitted.

Arrangement of ACK/NACK Information

A method of configuring a bit sequence {a₀, . . . , a_(Q−1)} of ACK/NACKinformation transmitted through a PUCCH is described. The bit sequencemay be an input bit-stream of channel coding for the ACK/NACKinformation.

(Method 1) A wireless device arranges an ACK/NACK bit preferentially(e.g., from a most significant bit (MSB)) for a cell in which a PDSCH isreceived in the ACK/NACK information.

An order of the ACK/NACK bits may conform to a predetermined rule (e.g.,a cell index order). However, the arranging of the ACK/NACK bits throughthe predetermined rule may result in a mismatch of the ACK/NACK bitarrangement between a wireless device and a BS when the wireless devicemisses a presence of a scheduled PDSCH in a specific cell. Therefore, aDL assignment index (DAI) may be included in DCI having a DL grant forscheduling the PDSCH.

The DAI may be divided into two types, i.e., a cell-DAI (c-DAI) and atime-DAI (t-DAI). The c-DAI may have a successively increasing value forPDSCHs scheduled for different cells in the same subframe.Alternatively, the c-DAI may have a successively increasing value forPDSCHs scheduled for different cells in different subframes. The t-DAImay have a value which increases for each subframe in which the PDSCH isscheduled for each cell.

The wireless device may arrange ACK/NACK bits in an order of the DAIvalue in the ACK/NACK information. If DCI having a DAI value smallerthan a received maximum DAI value is not received, it is regarded thatreception of the DCI corresponding to the missing DAI value has failed,and it may be processed that the ACK/NACK bit is NACK or DTX (a stateindicating that PDSCH reception has not be achieved). For example,assume that the received DAI values is {0, 1, 3, 4}. The wireless devicemay regards that reception of the DCI corresponding to DAI=2 has failed,and thus may process an ACK/NACK bit corresponding to DAI=2 as NACK orDTX.

The ACK/NACK bit corresponding to the received maximum DAI value may beprocessed as NACK or DTX.

Assume that the PUCCH format is designated by the DCI. If a size of theACK/NACK information determined based on the maximum DAI value received(or received PDSCH) is greater than a size of a payload of thedesignated PUCCH format, only information capable of being transmittedthrough the PUCCH format may be transmitted according to a determinedACK/NACK bit order. For example, if the size of the payload of thedesignated PUCCH format is 72 bits and the size of the ACK/NACKinformation obtained from the maximum DAI is 80 bits, only 72 bits outof 80 bits of ACK/NACK information may be transmitted through the PUCCHformat.

Since reception of the DCI including the PUCCH format indication may bein an unstable state, the wireless device may not transmit the entireACK/NACK information. Upon receiving a PDSCH for a PCell, only ACK/NACKinformation for the PDSCH may be transmitted through the PUCCH. Thewireless device may operate under the assumption that it has notreceived a corresponding PDSCH/PDCCH or all PDSCHs/PDCCHs (a PDSCH/PDCCHfor the PCell may be excluded) received in a corresponding subframe.Specifically, PDSCH decoding may not be performed, or PDSCH data may notbe stored in a DL HARQ buffer.

It may be adjusted that a cell having a specific feature has a lowpriority. For example, for an unlicensed cell operating in an unlicensedband which cannot be used exclusively in an LTE system, a DAI value isallowed to have a low priority so that an ACK/NACK bit of the unlicensedcell is arranged to be closed to a least significant bit (LSB).

FIG. 27 shows an example of selecting a PUCCH according to an embodimentof the present invention.

An ARI may indicate a PUCCH resource for another PUCCH format dependingon a range of a DAI. For example, assume that PUCCHy is used if thenumber of cells in which a PDSCH is received is less than or equal to L,and PUCCHz is used if it exceeds L. An ARI of DCI having a DAI value inthe range of 0 to (L−1) may indicate a PUCCHy resource, and an ARI ofDCI having a DAI value greater than or equal to L may indicate a PUCCHzresource. The PUCCHy may be used to transmit ACK/NACK information for aPDSCH corresponding to the DAI value in the range of 0 to (L−1), and thePUCCHz may be used to transmit ACK/NACK information for PDSCHs of allcells. Upon receiving the DCI having the DAI value greater than or equalto L, the wireless device may ignore an ARI of DCI having a DAI valueless than L.

In the example of FIG. 27, assume that PUCCHy is linked to a DAI valuein the range of 0 to 1, and the PUCCHz is linked to a DAI value in therange of 2 to 3. Since a DAI of a cell 0 is 0 and a DAI of a cell 1 is1, the PUCCHy is selected. An ARI of corresponding DCI designates aPUCCHy resource.

FIG. 28 shows another example of selecting a PUCCH according to anembodiment of the present invention. Since there are two or more DAIs,PUCCHz is selected by ignoring the DAIs when the number of DAIs is lessthan 2.

FIG. 29 shows another example of selecting a PUCCH according to anembodiment of the present invention. This is a case where reception ofDCI of a cell 1 has failed. Since there are two or more DAIs, PUCCHz isselected by ignoring the DAIs when the number of DAIs is less than 2.

In addition, when a plurality of resource blocks are allocated to thePUCCHz, the number of allocated resource blocks may be determinedaccording to the range of the received DAI value.

(Method 2) ACK/NACK bits for a plurality of serving cells are arrangedat predetermined positions.

A wireless device arranges ACK/NACK bits of a configured cell at aposition pre-assigned in each PUCCH format. The configured cell mayinclude only an activated cell, or may include an inactivated cell otherthan the activated cell.

For example, ACK/NACK bits corresponding to cells having a lowest cellindex among all configured cells may be arranged in the PUCCHy, andACK/NACK bits for all configured cells may be arranged in the PUCCHz.

Assume that the PUCCH format is designated by the DCI. Upon receiving aPDSCH of a cell in which the arrangement of the ACK/NACK bit is notdesignated, the wireless device may not transmit the ACK/NACK bitcorresponding to the PDSCH.

Since reception of the DCI including the PUCCH format indication may bein an unstable state, the wireless device may not transmit the entireACK/NACK information. Upon receiving a PDSCH for a PCell, only ACK/NACKinformation for the PDSCH may be transmitted through the PUCCH. Thewireless device may operate under the assumption that it has notreceived a corresponding PDSCH/PDCCH or all PDSCHs/PDCCHs (a PDSCH/PDCCHfor the PCell may be excluded) received in a corresponding subframe.Specifically, PDSCH decoding may not be performed, or PDSCH data may notbe stored in a DL HARQ buffer.

(Method 3) ACK/NACK compression is applicable according to the PUCCHformat.

If the PUCCH format is designated through DCI, the wireless device maytransmit ACK/NACK information for all cells configured in the designatedPUCCH format. Spatial bundling based on a logical-AND operation may beapplied to a plurality of ACK/NACK bits for a plurality of transportblocks received from each cell. Bundling based on the logical-ANDoperation may be applied to a plurality of ACK/NACK bits for a pluralityof transport blocks received in a plurality of subframes. When bundlingis applied, the number of ACK/NACK bits to be transmitted may bedecreased. ACK/NACK to which bundling is applied is called bundledACK/NACK.

If a payload size differs for each PUCCH format, whether to applybundling may be determined according to the payload size. For example,if PUCCHy is selected, the bundled ACK/NACK may be transmitted for apart of the entire cell (or entire DAI). If PUCCHz is selected, bundlingmay not be applied to the entire cell (or entire DAI). If there are notmany cells to be actually scheduled in comparison with the total numberof cells, a PUCCH format having a small payload size may be utilized toeffectively use a PUCCH resource.

If the PUCCH format has a payload size which differs depending on thePUCCH resource, whether to apply bundling may be determined depending onthe payload size. For example, if a PUCCHz resource 0 is selected,bundled ACK/NACK may be transmitted for a part of the entire cell (orentire DAI). If a PUCCHz resource 1 is selected, bundling may not beapplied to the entire cell (or entire DAI). If there are not many cellsto be actually scheduled in comparison with the total number of cells, acode rate of ACK/NACK information may be decreased to improve ACK/NACKtransmission performance.

Meanwhile, when the number of ACK/NACK bits to be transmitted in one ULsubframe is determined according to the number of DL subframesassociated with the UL subframe as in the TDD system, the selection ofthe PUCCH format according to the aforementioned embodiment may beconfigured selectively for each subframe. It is considered that asubframe X is configured to transmit ACK/NACK bits corresponding to X ormore DL subframes and a subframe Y is configured to transmit Y or moremaximum ACK/NACK bits. The subframe X and/or the subframe Y may be asubframe to which PUCCH selection is applied. A PUCCHy resource and aPUCCHz resource may be allocated in the subframe X and/or the subframeY, and PUCCHy or PUCCHz may be selected according to a size of ACK/NACKinformation or an indication of DCI. In the other subframes, ACK/NACKmay be transmitted through PUCCHx or PUCCHy or PUCCHz without theselection of the PUCCH format.

An ARI of the DCI corresponding to the ACK/NACK transmitted in thesubframe to which the PUCCH selection is applied may designate which onewill be used among a plurality of candidate PUCCH resources. The numberof bits of the ARI of the DCI corresponding to the ACK/NACK transmittedin the subframe to which the PUCCH selection is applied may be equal toor greater than the number of bits of an ARI of DCI corresponding toACK/NACK transmitted in a subframe to which the PUCCH selection is notapplied.

A first ARI of DCI corresponding to a subframe for selecting one ofPUCCHy and PUCCHz may designate M+N states. M denotes the number ofconfigured PUCCHy resources, and N denotes the number of configuredPUCCHz resources. A second ARI of DCI corresponding to a subframe notsupporting PUCCHz has the same number of bits as the first ARI, but maydesignate only M states.

Determination of ACK/NACK Payload Size

When N DL cells are configured in the existing LTE system and when aPUCCH format 3 is used, ACK/NACK bits corresponding to the N DL cellsare all transmitted always. A size of an ACK/NACK payload of the PUCCHformat 3 is determined according to the number of configured all DLcells. However, even if the number of configured cells is great, thenumber of cells in which actual PDSCH data is scheduled may be less thanthat number.

Therefore, it is proposed a method of determining a size of an ACK/NACKpayload of a PUCCH format in every subframe by using a set of sizes oflimited ACK/NACK payloads. A PUCCH format to which the presentembodiment is applied may be PUCCHz or PUCCHy.

(Method 1) A size of an ACK/NACK payload is determined according to thenumber of scheduled cells.

A cell in which PDSCH data is scheduled is called a scheduled cell. Thesize of the ACK/NACK payload may be determined according to the numberof scheduled cells.

A size n, of available ACK/NACK payloads capable of being transmittedthrough the PUCCH format may be limited to a specific set {n₁, n₂, . . ., n_(P−1), n_(P)}. Herein, n₁<n₂ . . . <n_(P−1)<n_(P). When there is aneed to transmit m-bit ACK/NACK information, the wireless device maydetermine a minimum value less than m to an ACK/NACK payload size n_(p).n_(p) and m may be set to the number of bits to be subjected to ACK/NACKfeedback or the number of cells to be subjected to ACK/NACK feedback.The number of scheduled cells may imply the number of cellscorresponding to a maximum DAI value received by the wireless device.However, since the number of scheduled cells may be mismatched betweenthe wireless device and the BS due to a PDCCH reception failure or thelike, the BS may attempt decoding on a size of a plurality of ACK/NACKpayloads.

If there is a PDSCH having no DAI (e.g., a PDSCH or the like transmittedwithout a PDCCH), the size of the ACK/NACK payload may be determined inthe following manner.

First, a value obtained by adding the number of PDSCHs having no DAI tothe number of PDSCHs calculated as the DAI value is set to m, and thesize of the ACK/NACK payload is determined.

Second, m is set according to the number of PDSCHs calculated as the DAIvalue, and the number of PDSCHs having no DAI is added to m to determinethe ACK/NACK payload size.

(Method 2) The size of the ACK/NACK payload is determined according tothe scheduled cell group.

A cell configured for a wireless device is divided into P groups, and asize of a available ACK/NACK payload that can be transmitted through aPUCCH format is limited to {n₁, n₂, . . . n_(P−1), n_(P)}. Herein, n₁<n₂. . . <n_(P−1)<n_(P)). n_(j) implies a size of an ACK/NACK payloadcorresponding to a cell belonging to groups 1, 2, . . . , j, that is,from a 1^(st) group to a j-th group.

The wireless device determines an ACK/NACK payload size corresponding ton_(j) when the cell group is at most the j-th group, and transmitsACK/NACK information for cells corresponding to the 1^(st) group to thej-th group. However, since the number of scheduled cells may bemismatched between the wireless device and the BS due to a PDCCHreception failure or the like, the BS may attempt decoding on a size ofa plurality of ACK/NACK payloads.

A minimum size n₁ in the set of payload sizes is equal to or greaterthan the minimum number of ACK/NACK bits (or ACK/NACK payload sizecorresponding to the minimum number of scheduled cells) that can betransmitted by the wireless device through the PUCCH format. The maximumsize n_(p) is greater than or equal to the maximum number of ACK/NACKbits (or an ACK/NACK payload size corresponding to the maximum number ofscheduled cells) that can be transmitted through the PUCCH format. n_(p)may be a size of an ACK/NACK payload corresponding to the total numberof cells configured for the wireless device. n_(p) may be a size of anACK/NACK payload corresponding to the total number of activated cellsconfigured for the wireless device.

Now, selection of a PUCCH format based on a DAI and ACK/NACK informationtransmission will be described.

DCI may include a DAI and a total DAI. The total DAI may be a valuecapable of estimating the total number of DL grants transmitted by a BS(or the total number of PDSCHs transmitted by the BS). A selected PUCCHformat may have a smallest maximum payload greater than the number ofbits of ACK/NACK information corresponding to the total number of DLgrants estimated from the total DAI. An ARI may indicate a resource of adetermined PUCCH format.

The total DAI may be expressed by one value corresponding to ‘ACK/NACKbits more than (exceeding) X bits’ and one or more values correspondingto ‘ACK/NACK bits less than (below) X bits’. The X bit is a boundarypoint at which CRC is attached to a bit-stream of ACK/NACK information,and it is assumed that the CRC is not attached if the number of bits ofACK/NACK information is less than (below) X bits. Since the CRC isattached when the number of ACK/NACK bits to be transmitted is more than(exceeds) X bits, the BS may determine the ACK/NACK size by performingCRC checking on the number of available ACK/NACK bits. The CRC is notattached when ACK/NACK information less than (below) X bits istransmitted. Therefore, the wireless device may transmit ACK/NACKinformation of which the number of bits is designated by the total DAI.

As described above, the c-DAI has a successively increasing value forthe PDSCH scheduled for different cells, and the t-DAI may have a valuewhich increases for each subframe in which a PDSCH is scheduled for eachcell. In addition, the cc-DAI is a value counted by being included inDCI of all subframes and all cells to be scheduled.

FIG. 30 shows an example of a cc-DAI. Assume that there are two cells,i.e., cell 0 and cell 1, and there is DCI having a DL grant for eachsubframe. In the same subframe, a cell having a low cell index isprioritized, and the cc-DAI is counted. In the present specification,the DAI may include the cc-DAI.

Assume that information regarding a size of an ACK/NACK payload isincluded in DCI to be scheduled. When ACK/NACK information for aplurality of PDSCHs to be transmitted through M subframes is transmittedthrough one UL subframe as in the TDD system, a BS may not be able todetermine the ACK/NACK payload size until PDSCH scheduling is completefor M subframes. If the determining of scheduling for the M subframes isnot complete until a DL grant is configured for a first subframe amongthe M subframes, the ACK/NACK payload size may differ depending on theDL grant. Therefore, the following method is proposed.

-   -   The wireless device may select a PUCCH format or may configure        an ACK/NACK payload through DCI in a most recently received        subframe among the M subframes.    -   The wireless device may select a PUCCH format or configure the        ACK/NACK payload according to a cell group corresponding to the        entire DCI received among the M subframes or an indicated        ACK/NACK payload.    -   The DL grant may include a DAI and a total DAI. The wireless        device may select the PUCCH format or configure the ACK/NACK        payload according to an indication of a DL grant corresponding        to a received last DAI value (or a greatest DAI value). The        wireless device may select the PUCCH format or configure the        ACK/NACK payload according to an indication of a DL grant        corresponding to a received last total DAI value (or a greatest        total DAI value).    -   The wireless device may select the PUCCH format or configure the        ACK/NACK payload according to an accumulation value of all        received DAIs. The wireless device may select a PUCCH format or        configure an ACK/NACK payload according to an accumulation value        of all received total DAIs.

The number of ACK/NACK bits transmitted through PUCCHz in theaforementioned methods may be determined according to the number ofscheduled cells, a cell ID, a cell group ID, or the like for eachsubframe. The number of ACK/NACK bits to be transmitted through PUCCHymay be fixed. The wireless device may transmit NACK (or DTX) in a placeof an ACK/NACK bit corresponding to cells in which a PDSCH for actuallyfeeding back ACK/NACK is not scheduled. In particular, it may be appliedto a case where CRC is not attached to an ACK/NACK bit to be transmittedthrough PUCCHy, and there is an advantage in that the BS does not haveto separately detect a size of ACK/NACK to be transmitted throughPUCCHy.

ACK/NACK Information Classification in the Same ACK/NACK Payload Size

Even if a PUCCH format selected by a wireless device and an ACK/NACKpayload size of the PUCCH format are determined, if a configuration ofACK/NACK information actually transmitted is different, the wirelessdevice may need to inform a BS of a method of configuring the ACK/NACKinformation.

For example, assume that there is a cell group A and a cell group B, andthat the wireless device selects a PUCCH format to transmit an ACK/NACKaccording to a cell group for receiving a PDSCH. PUCCHy is selected whenPDSCH is received only through the cell group A, and the wireless devicetransmits the ACK/NACK information through the PUCCHy. In this case, thewireless device may transmit additional information on a PUCCH to informa certain cell group of which ACK/NACK information is informed by thePUCCHy.

A plurality of transport blocks may be transmitted on one PDSCH throughmultiple input multiple output (MIMO). Regarding ACK/NACK spatialbundling, the following method may be applied to PUCCH selection. ‘Nb’denotes the number of ACK/NACK bits to be transmitted when spatialbundling is not applied in a UL subframe, and ‘Nr’ denotes the number ofACK/NACK bits to be transmitted when spatial bundling is applied in theUL subframe.

-   -   A PUCCH format capable of transmitting at least Nb bits (with a        smallest payload size) is selected, and spatial bundling is not        applied. When a PUCCH format with a greatest payload size cannot        accommodate the Nb bits, the spatial bundling is applied. In        addition, the PUCCH format is selected on the basis of Nr bits.    -   A PUCCH format capable of transmitting at least Nr bits (with a        smallest payload size) is selected. If the selected PUCCH format        cannot accommodate at least Nb bits, spatial bundling is not        applied. Otherwise, the spatial bundling is applied.

The selected PUCCH format may include additional information indicatingwhether spatial bundling is applied to ACK/NACK information. When thespatial bundling is applied according to the required number of ACK/NACKbits, the selected PUCCH format may include additional informationindicating whether the spatial bundling is applied to the ACK/NACKinformation. The additional information may be transmitted in a form ofCRC masking of the ACK/NACK information, a scrambling sequence of theACK/NACK information, a sequence masked to DMRS of the PUCCH, or thelike.

Assume that Nbmax denotes the maximum number of ACK/NACK bits that canbe transmitted in the selected PUCCH format. If Nr<=Nbmax<Nb, thespatial bundling may be applied, and if Nb<Nbmax, the spatial bundlingmay not be applied. The number of bits of the ACK/NACK informationvaries depending on whether the spatial bundling is applied, and thismay cause complexity of ACK/NACK decoding of a BS. In order to avoidthis, additional bits of Nb-Nr may be added to the ACK/NACK informationwhen the spatial bundling is applied. That is, the PUCCH format alwaystransmits information of Nb bits regardless of whether the spatialbundling is applied. The Nb-bit ACK/NACK information or the Nr-bitACK/NACK information may be selected on the basis of a scheduled cell,an activated cell, or a configured cell.

FIG. 31 is a block diagram showing a wireless communication systemaccording to an embodiment of the present invention.

A wireless device 50 includes a processor 51, a memory 52, and atransceiver 53. The memory 52 is coupled to the processor 51, and storesvarious instructions executed by the processor 51. The transceiver 53 iscoupled to the processor 51, and transmits and/or receives a radiosignal. The processor 51 implements the proposed functions, procedures,and/or methods. In the aforementioned embodiment, a UL control operationof the wireless device may be implemented by the processor 51. When theaforementioned embodiment is implemented with a software instruction,the instruction may be stored in the memory 52, and may be executed bythe processor 51 to perform the aforementioned operation.

A BS 60 includes a processor 61, a memory 62, and a transceiver 63. TheBS 60 may operate in an unlicensed band. The memory 62 is coupled to theprocessor 61, and stores various instructions executed by the processor61. The transceiver 63 is coupled to the processor 61, and transmitsand/or receives a radio signal. The processor 61 implements the proposedfunctions, procedures, and/or methods. In the aforementioned embodiment,an operation of the BS may be implemented by the processor 61.

The processor may include Application-Specific Integrated Circuits(ASICs), other chipsets, logic circuits, and/or data processors. Thememory may include Read-Only Memory (ROM), Random Access Memory (RAM),flash memory, memory cards, storage media and/or other storage devices.The RF unit may include a baseband circuit for processing a radiosignal. When the above-described embodiment is implemented in software,the above-described scheme may be implemented using a module (process orfunction) which performs the above function. The module may be stored inthe memory and executed by the processor. The memory may be disposed tothe processor internally or externally and connected to the processorusing a variety of well-known means.

In the above exemplary systems, although the methods have been describedon the basis of the flowcharts using a series of the steps or blocks,the present invention is not limited to the sequence of the steps, andsome of the steps may be performed at different sequences from theremaining steps or may be performed simultaneously with the remainingsteps. Furthermore, those skilled in the art will understand that thesteps shown in the flowcharts are not exclusive and may include othersteps or one or more steps of the flowcharts may be deleted withoutaffecting the scope of the present invention.

What is claimed is:
 1. A method for transmitting apositive-acknowledgement/negative-acknowledgement (ACK/NACK) in awireless communication system, the method performed by a wireless devicecomprising: receiving a plurality of downlink (DL) grants on a pluralityof serving cells, each DL grant including a counter downlink assignmentindex (DAI) and an ACK/NACK resource indicator (ARI), the counter DAIindicating an accumulative number of PDSCHs received by the wirelessdevice for a corresponding DL grant; receiving a plurality of physicaldownlink shared channels (PDSCHs) associated with the plurality of DLgrants; selecting one of a plurality of sets of PUCCH resources based ona payload size of uplink control information (UCI), the UCI includingACK/NACK bits for the plurality of PDSCHs; determining a PUCCH resourcewithin the selected set of PUCCH resources based on an ARI included inthe most recently received DL grant among the plurality of DL grants;and transmitting the UCI by using a PUCCH format associated with thedetermined PUCCH resource.
 2. The method of claim 1, wherein each DLgrant further includes a total DAI, the total DAI indicating a totalnumber of PDSCHs received by the wireless device for a corresponding DLgrant.
 3. The method of claim 1, wherein the ARI has at least two bits.4. The method of claim 1, wherein each set of PUCCH resources includes aplurality of PUCCH resources.
 5. The method of claim 4, wherein eachPUCCH resource includes information on a PUCCH format and a resourceblock assigned to the PUCCH format.
 6. An apparatus for transmitting apositive-acknowledgement/negative-acknowledgement (ACK/NACK) in awireless communication system, the apparatus comprising: a transceiverconfigured to transmit and receive a radio signal; and a processoroperatively coupled to the transceiver and configured to: control thetransceiver to receive a plurality of downlink (DL) grants on aplurality of serving cells, each DL grant including a counter downlinkassignment index (DAI) and an ACK/NACK resource indicator (ARI), thecounter DAI indicating an accumulative number of PDSCHs received by thewireless device for a corresponding DL grant; control the transceiver toreceive a plurality of physical downlink shared channels (PDSCHs)associated with the plurality of DL grants; select one of a plurality ofsets of PUCCH resources based on a payload size of uplink controlinformation (UCI), the UCI including ACK/NACK bits for the plurality ofPDSCHs; determine a PUCCH resource within the selected set of PUCCHresources based on an ARI included in the most recently received DLgrant among the plurality of DL grants; and control the transceiver totransmit the UCI by using a PUCCH format associated with the determinedPUCCH resource.
 7. The apparatus of claim 6, wherein each DL grantfurther includes a total DAI, the total DAI indicating a total number ofPDSCHs received by the wireless device for a corresponding DL grant. 8.The apparatus of claim 6, wherein the ARI has at least two bits.
 9. Theapparatus of claim 6, wherein each set of PUCCH resources includes aplurality of PUCCH resources.
 10. The apparatus of claim 9, wherein eachPUCCH resource includes information on a PUCCH format and a resourceblock assigned to the PUCCH format.